The phrase "assure herself" is correct and usable in written English.
It can be used when someone is seeking to confirm or guarantee something for their own peace of mind or confidence.
Example: "Before making the final decision, she needed to assure herself that all the facts were in order."
Alternatives: "convince herself" or "satisfy herself".
Her face was glazed in tears, but she stared intently at me as I prepared to sign the papers, as if to assure herself I knew what I was doing.
All that remains is the W.T.A. Championships, the elite eight-woman grand finale in Istanbul, and all Azarenka needs to assure herself of being No. 1 at season's end are two victories in the round-robin phase of the competition.
Many Democrats have long argued that Mrs. Clinton had all the prerequisites to assure herself a clear path to her party's nomination in 2008, including money, high poll ratings with Democrats, star power and a formidable political operation.
She had opened the door and gone down the steps just once since Rich had died, to see that no lights had been left on, and to assure herself that the fuse switches were there, with labels written beside them to tell her which controlled what.
The whole day was full of surprises and everything came to a fantastic climax as Gibbons--literally the hometown hero being a Londoner--managed to somehow defeat the top-seeded world champion Audrey Tcheumeo in the semifinals and assure herself a medal.
The top three Europeans in each weight division in Qinhuangdao qualify for the Games, and Jonas was the first Briton to secure her place - as well as assure herself of at least a world bronze medal.
'This is a test,' she assured herself with a smile.
And she also assures herself and others that, spiritually, she is allowed an unburdening.
Hantuchova assured herself of breaking into the top 20 in the ranking for the first time.
A restaurant owner lets slip her fear of war while serving breakfast, but quickly assures herself the cartel will adjust.
She is poised to make a triumphant return later this month when she resumes her presidential duties fulltime, assuring herself a lift in already sky-high approval ratings.
